TOL J VAN, KUNTZE E, REGENSBURG BA, REGENSBURG CA & SLUIS F VAN DER (1979) comparison of methods to estimate the number of breeding pairs of the Tufted Duck Aythya fuligula. LIMOSA 52 (1): 12-21.

Tufted Duck Aythya fuligula In three differently structured reservoirs in the dene area Meijendel between Wassenaar and 's-Gravenhage (Zuid-Holland) (fig. 1) the number of breeding pairs of the Tufted Duck Aythya fuligula was estimated by different methodsin 1975. Estimation by (a) counting pairs present in the first half of May, (b) counting drakes in the breeding season and (c) counting ducks with pulli gave an underestimation for one reservoir and an overestimation of c. 50% for the other ones when compared with the results of counting nests (table 1 and fig. 3). There is good evidence that this is caused by a change in habitat-selection of the pairs with the onset of the breeding season. They migrate from the open water to places with small dimensions, e.g. islands with coves. An acceptable method in the Netherlands in order to estimate the breeding population is counting pairs in an area as large as possible in the second week of May..

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